The present invention relates to a sensor device for detecting mechanical deformation of a component.
Although applicable to any components, the present invention and the principles on which it is based are explained with respect to a component in the automotive area.
In general, for protection of occupants in automotive engineering, it is necessary to promptly detect an impact or collision of the motor vehicle with an obstacle and to activate proper passenger safety applications. Deformation sensor devices are frequently also used in addition to acceleration sensor devices.
According to the related art, the deformation sensor devices that are used are based on metal-layer strain gauges. Metal-layer strain gauges are riveted to a door-reinforcing element of the vehicle, for example, and function as extra detectors in addition to the peripheral side impact-detecting acceleration sensors for detecting deformation of the door as a result of impact of same with an obstacle; shorter deployment times are to be made possible for the corresponding safety applications.
Typical metal-layer strain gauges are made of constantan or nickel-chromium layers, for example. Mechanical deformation of the metal-layer strain gauge causes its electric resistance to change. The quotient of the percentage change in resistance and percentage change in length is known as the k factor and amounts to approximately 2 for the examples given above. Metal-layer strain gauges are usually dimensioned so as to yield a scaling factor of 2 mV/V in a complete measurement range. However, this is only a low useful signal.
The problem on which the present invention is based is thus in general that because of the low useful signal, on-site pre-amplification and a suitable digital interface are necessary for transmission of the corresponding change in resistance data to a central unit.
The sensor device according to the present invention has the advantage in comparison with the known approach that a cost-optimized deformation sensor device for side impact detection, for example, is feasible, supplying a sufficiently large signal for the change in resistance due to mechanical deformation, this signal being transmittable as an analog signal to a central unit for analysis.
The idea on which the present invention is based is that the sensor device has a deformation device, which has a deformable polysilicon part that undergoes a change in electric resistance when deformed, and it has an electric conductor arrangement for analog transmission of change in resistance data concerning the polysilicon part from the deformation device to a central unit.
In the event of deformation of the polysilicon part, a useful signal is obtained on the basis of the change in resistance, which is large enough for analog transmission to a central unit even without pre-amplification. This makes it possible to eliminate expensive additional electronic components and to manufacture a more compact and cost-optimized sensor device.
According to a preferred refinement, the polysilicon part is designed as a polysilicon strain gauge (DMS). It is often sufficient to detect deformation along a certain segment.
According to another preferred refinement, the polysilicon strain gauge has a k factor of up to 40. This yields such a large change in resistance that the useful signal is transmittable as an analog signal to a central unit without preamplification.
According to another preferred refinement, due to suitable doping of the polysilicon strain gauge, it has a k factor which is essentially independent of the temperature of the polysilicon strain gauge. Due to this lack of thermal sensitivity of the k factor, a greater reliability of the measured values is achieved.
According to another preferred refinement, the deformation device has a carrier on which there is a Kapton (polyimide) film or the like on which in turn the polysilicon strain gauge is glued and into which the corresponding electric lines or line contacts may be integrated. This is an especially inexpensive design which is simple to manufacture.
According to another preferred refinement, contact points or bond pads for contacting the corresponding electric connections are situated on the Kapton film.
According to another preferred refinement, the deformation device has a gelatinous cover which provides both mechanical and electrical protection.
According to another preferred refinement, the deformation device is situated horizontally in a door-reinforcing element of a vehicle. For a one-dimensional deformation measurement of the door-reinforcing element, for example, it is sufficient to measure the mechanical deformation along a certain line.
According to another preferred refinement, the polysilicon strain gauge is wired as a rheostat.
According to another preferred refinement, the change in resistance data is transmittable over two twisted conductors to the central unit. The twisted conductors prevent electromechanical interference from being injected.
According to another preferred refinement, the sensor device has at least one filter device for high-pass filtering of predetermined interference quantities in particular.
Since the analysis of crash signals is performed purely dynamically in the event of a collision with an obstacle, other types of high-frequency dynamic interference must also be minimized, since they may under some circumstances cause a faulty analysis of the measurement.